Mirey Brook is a 6.5-mile-long (10.5 km) stream in northern Massachusetts and southwestern New Hampshire in the United States. It is a tributary of the Ashuelot River, itself a tributary of the Connecticut River, which flows to Long Island Sound. State Route 78 follows Mirey Brook from its confluence with Mountain Brook to its mouth at the Ashuelot. A major tributary of Mirey Brook is Roaring Brook, which enters from the east near the village of Scotland, New Hampshire.